1. Field of the Invention
The present invention relates generally to cleaning contaminants such as oil and grease from the surface of substrates such as metal and plastic parts using a biological cleaning system which cleans the parts and digests the contaminants so that the cleaning solution is maintained in an active state over an extended cleaning time period and, in particular, to the use of a combination cleaning and treating bath and/or a recycle pre-treatment and/or post-treatment bath to provide an efficient and cost effective integrated biological cleaning system.
2. Description of Related Art
While microorganisms have been used for many years to digest oil from wastes and spills, the integration of biodegradation with aqueous cleaning for metal and other material finishing applications is a relatively recent process. Mild alkaline emulsifying cleaners that operate at relatively low temperatures are now used to integrate the removal of oil and particulates in a parts cleaning operation with biological digestion of the residues. The system is essentially self-regulating, since the microbial activity will adjust itself to the amount of removed oil and grease present in the system.
In a typical system used in the metal finishing industry, an alkaline cleaning solution and control system is employed that utilizes microbes in the solution to consume the oil/grease that is removed from parts during the cleaning process. The system operates at relatively low temperatures (104°F.-131°F.) (40° C.-55° C.) and a pH range of 8.8-9.2, which is a viable habitat for the microorganisms. The cleaning process actually takes place in two separate operations. When parts come in contact with the solution, the oil and impurities are emulsified into micro-particulates. The micro-particulates are then consumed by microorganisms which are present in the bath. The microbe consumption of the oil present in the bath, as its food source, results in the production of CO2 as a by-product. The microbes are naturally present in industrial oils and greases, and the main species responsible for biodegradation has been identified as pseudomonas stutzeri, a microorganism found in soil and water.
In one process operation, the cleaning solution from a cleaning tank is pumped continuously between a separator module and the cleaning tank. This operation is run in a continuous mode without interruptions for solution dumping and new solution make-up. As a result of the dynamics of the process and the re-circulation of the bath solution, the consumption of oil by the microbes occurs throughout the biological degreasing system. For an efficient operation the oil must be emulsified and oil must be present at all times to keep an active population of microorganisms. In the case of a longer interruption that may be conducive to the total depletion of the oil present in the system, to keep the microbes alive it is necessary to render them dormant typically by increasing the pH to 10.5 or alternatively, to feed them with small amounts of oil during the down time.
The typical system is managed by a control unit which controls the process parameters such as temperature and pH, and the replenishment of surfactants and nutrients, maintaining the chemical and biological equilibrium. It is possible to operate the system without downtime for extended periods (up to many years), eliminating the need of dumping spent cleaning solutions. The enhanced productivity and the reduced use of chemicals and water have made the system well suited to fulfill the present needs of the industry.
Biological cleaning systems offer many advantages over conventional chemical cleaners. The life of the cleaning solutions have been lengthened to the point that today there are many operations where the original cleaning solution is in use many years after installation. Biological cleaning process also creates practically no solid or liquid waste that requires treatment and disposal. The degreasing processes are also more effective since the parts are treated with a cleaning solution that is continuously rejuvenated and always has about the same composition and a consistent oil removal ability. Biological cleaning systems offer major economies savings in chemicals, labor, waste disposal and energy costs.
The biological cleaning systems used today have been adapted to the requirements of a broad range of industrial applications, and currently the process is used in electroplating, painting, powder coating anodizing and general metal and plastic working operations.
While biological cleaning has proven its effectiveness in a large number of installations, under certain conditions the parts to be cleaned must be pre or post treated and/or are not totally cleaned since contaminants still remain on the surface. This requires further steps to specially treat or clean the part which affects the cost effectiveness of the total part treating process. One particular application is the need to provide a clean, phosphated part for further processing, such as painting. This process now requires a number of non-integrated steps. In another application, parts which have been cleaned or partially cleaned in a biological cleaner are now post-treated by electrocleaning in an electrocleaner bath. This process likewise now requires a number of non-integrated steps.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for cleaning substrate surfaces in which the parts are cleaned to commercial standards and which substrates may also be pre or post treated, i.e., phosphated, electrocleaned, etc. for further downstream processing.
It is another object of the present invention to provide a biological cleaning system for cleaning substrate surfaces which provides parts cleaned to commercial standards and which parts may also be pre or post treated, i.e., phosphated, electrocleaned, etc. for further downstream operations.
In another object of the present invention a method and apparatus are provided for providing cleaned, treated parts in a single step cleaning and treating bath such as a detergent phosphating bath, which bath may be used with or without the pre-or post-treatment steps described above.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.